The explanation behind megafauna extinction in Australia is a debate that has raged on for decades, and the major hypotheses can be divided into two camps: climate change or human driven. It is known that humans arrived in Australia at least by 47,000 years ago, which overlaps with the last appearance of megafauna (50-40,000 years ago). This debate is difficult to resolve because there is no direct evidence of human predation on megafauna like giant wombats and enormous flightless birds similar to what is found in North America or Europe—no spear points embedded in mastodon bone or cut marks that were clearly made by sharp tools have been found at localities Down Under.

The lack of evidence surrounding human predation means it must have been climate change, right? The issue with this is that there does not seem to be any significant climate change around the time that megafauna went extinct on the continent besides an apparently minor trend towards drier climates. This is in stark contrast to a clear major climate change that happened in Eurasia and North America when woolly rhinos and woolly mammoths became extinct—the glacial landscapes they were adapted to warmed up and were replaced with extensive forests.

The lack of “kill sites” for megafauna in Australia has always been a missing piece of the extinction puzzle—perhaps until now. While no typical “kill site" has been discovered, Miller and his team have uncovered over 200 archaeological collections across Australia that contain burnt eggshell fragments of an extinct 200kg flightless bird called Genyornis newtoni. Miller explains these blackened eggshell fragments are critical for understanding human interactions with megafauna in Australia: "We consider this the first and only secure evidence that humans were directly preying on now-extinct Australian megafauna.”

Photographs of the burnt eggshells on the left side of the panel. The right side indicates the degradation of the amino acids across the transect in the eggshell, indicating it was not burned in a forest fire but rather over a human-created fire.(Figure 2 from Miller et al. 2016 in Nature Communications, CC BY 4.0)

The irregular blackening patterns on the eggshells seem to indicate these fragments were burned in a fire rather than during a forest fire. To confirm this hypothesis, Miller subjected the eggshells to an amino-acid analysis that measures how degraded the proteins on the eggshell surface are. This analysis revealed that over the surface of the eggshell the amino acid degradation was graded, meaning it was differentially heated—a pattern resembling an egg being turned over a fire rather than being scorched by a large wildfire.

Burnt eggshells were most commonly found in the sand dunes of Western Australia, but at none of the locations were they associated with stone tools or any other indicators humans were eating them. Dating reveals the eggshells to be between 53.9 and 43.4 ka, so they are from right around the time Genyornis went extinct. But even though humans were eating their eggs, did they cause their extinction? It may seem far-fetched but previous research has shown the impact of humans on large long-lived vertebrates with low reproductive rates can be immense, even with modest hunting practices.

This new find will likely continue to ignite more controversy, as it does not settle the extinction question once and for all. Although it does indicate that humans did indeed interact with megafauna, and the possibility for more evidence to be discovered still exists.

Shaena Montanari is a paleontologist and science communicator. Follow her on Twitter at @DrShaena for the latest natural history and fossil news.